allow fixture_type to be null in fixture API
allow fixture_type to be null in fixture API

SEL-Columbia/commcare-hq,dimagi/commcare-hq,qedsoftware/commcare-hq,qedsoftware/commcare-hq,qedsoftware/commcare-hq,puttarajubr/commcare-hq,dimagi/commcare-hq,dimagi/commcare-hq,puttarajubr/commcare-hq,SEL-Columbia/commcare-hq,puttarajubr/commcare-hq,SEL-Columbia/commcare-hq,qedsoftware/commcare-hq,dimagi/commcare-hq,dimagi/commcare-hq,qedsoftware/commcare-hq,puttarajubr/commcare-hq